Mesoscale Interactions in Solid-State Electrodes

Lithium-ion batteries (LIBs) are at the forefront of the energy storage technology for portable electronic devices and are playing a pivotal role in vehicle electrification. As the conventional LIBs consisting of a graphite anode and a transition metal oxide cathode approach their theoretical energy density limits, significant research efforts are being made towards developing next-generation batteries that can meet the ever-increasing energy density demands. In this regard, solid-state batteries (SSBs), employing lithium metal anode and a composite cathode, have garnered significant attention as a promising alternative to conventional LIBs, offering enhanced energy density and safety. However, the development of stable, high-performance SSBs is hindered by several interfacial and chemo-mechanical challenges due to solid-solid nature of interfaces. Limited solid-solid contact between the interacting species leads to severe transport and reaction limitations, which exacerbate during cycling due to progressive delamination at the interfaces. Such a phenomenon also results in current constriction at the remaining point contacts, which ultimately leads in the formation of electrochemical and mechanical hotspots within the SSB, impacting both the rate capability and cycling performance.

In this thesis, a comprehensive mesoscale investigation of solid-state battery (SSB) cathode architectures will be presented, elucidating the complex interplay between microstructure, kinetic-transport interactions and chemo-mechanical coupling. By examining the key limiting mechanisms that manifest at various SSB cathode microstructural regimes, a mechanistic design map highlighting the dichotomy in reaction and ionic/electronic transport limitations will be established. The impact of cathode microstructural heterogeneity on spatio-temporal dynamics, thermo-electrochemical behavior, and lithium metal anode stability will be revealed. In addition, the impact of stack pressure on solid-state cathode performance will be studied and how stack pressure influences the microstructure-dependent reaction and transport interactions will be delineated. Lastly, this thesis will investigate crystallographically oriented dense cathode architectures for high energy density SSBs, providing critical insights into their performance limitations and potential pathways for optimization. Overall, the dissertation will focus on the fundamental insights into the mesoscale behavior of the solid-state cathodes and establish the mechanistic pain points and design guidelines for consideration in the future development of improved SSB cathode architectures.